1. Field of the Invention
The present invention relates to a method and apparatus for making a composite, such as a polymer concrete wherein the concrete has a low percentage of resin therein, such as below ten percent (10%) by weight resin.
2. Description of the Prior Art
Heretofore it has been known in the production of composite articles, which are defined as articles made from a filler material, e.g., a particulate material, and a binder such as cement and water or a liquid thermosetting resin, that polymer concrete articles such as those made using a polymer or monomer resin as a binder have desirable properties, particularly high strength over cement based concrete articles.
However, the cost of the polymer or monomer resin relative to the particulate material is very high and typically the amount of polymer in a polymer concrete article costs twenty times more than the particulate material or aggregate in the polymer concrete article. As a result, the cost of polymer concrete articles has prevented more widespread use of polymer concrete articles.
With present manufacturing methods and apparatus for the manufacture of polymer concrete articles, it is very difficult to manufacture a concrete article with less than ten percent (10%) by weight resin in the article if the filler mix contains many fine particles.
The problem is that when the amount of the binder, e.g., resin, is very low, it is very difficult to mix the binder with the particulate material or aggregate because there is insufficient liquid to wet the surface of the particles of the filler mixture. An analogy would be the mixing of pancake mix, which calls for one cup of water, with one teaspoon of water. It may be possible eventually to obtain substantial mixing and partial or sufficient wetting throughout the mixture but it will take a long time to effect such mixing.
Thus, prior attempts to produce polymer concrete articles with a low percentage of resin have been self-defeating since, to obtain the low resin polymer concrete article, one had to spend several hours mixing the low content resin with the particulate matter prior to casting, heating, if necessary, and setting, polymerization, gelling or curing of the thermosetting resin based polymer concrete material.
Examples of methods and apparatus for producing polymer concrete are disclosed in German Offenlugungsschrift 32 07 432; and, 36 37 755. The polymer concrete machines disclosed in these Published German patent applications are manufactured by Respecta Baumaschinen-Gesellschaft MBH of Dusseldorf, West Germany.
Furthermore, process for casting products having a thermosetting resin binder therein are disclosed in U.S. Pat. Nos. 4,473,673 and 4,652,596.
Also, it is known from U.S. Pat. No. 3,633,880 to place a vacuum on an extrusion device for venting volatile elements from an extrudate.
Additionaly, polymer concrete systems have been proposed wherein a low resin percentage is obtained in the polymer concrete product by a method of over vibration of a mold filled with a mixture of resin and filler causing filler particles to settle to the bottom of the mold thereby displacing some of the resin binder which forms a resin-rich layer at the top of the mold cavity, after the resin has set (polymerized). This resin rich layer is then cut off and thrown away thereby wasting the excess resin required for mixing.
As will be described in greater detail hereinafter, the method and apparatus of the present invention provide a solution to the problem of obtaining a low cost polymer concrete article having a low percentage by weight of resin binder therein. As will be described in greater detail hereinafter, this is achieved by first mixing a quantity of resin binder with a non-reactive diluent. Then, the resulting liquid comprising diluent and resin is mixed with particulate material/aggregate, which can be, for example, sand and gravel. A catalyst can be added and the mixture is then thoroughly mixed and passed into an eduction chamber. The eduction chamber can include a screw type agitator which moves the mixture through the chamber while heat is supplied to the chamber and/or a vacuum is placed on the chamber to withdraw volatilized diluent This is done prior to supplying the mixture to a mold or forming station. Then, the mixture is supplied to a forming station where an article is shaped, formed or molded and more heat can be applied to the mixture to heat it to the setting temperature determined by the resin and catalyst mixture, which is greater than the temperature of any heat supplied to the eduction chamber.